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The fabrication of hollow ZrO2 nanoreactors encapsulating Au-Fe2O3 dumbbell nanoparticles for CO oxidation dagger
No full textNanosized Au catalysts suffer from serious sintering problems during synthesis or catalytic reactions at high temperatures. In this work, we integrate dumbbell-shaped Au-Fe3O4 heterostructures into hollow ZrO2 nanocages to make Au-Fe2O3@ZrO2 yolk-shell nanoreactors with high activity as well as ultra-high sintering resistance for high-temperature CO oxidation. The synthesis starts with the fabrication of a (Au-Fe3O4)@SiO2@ZrO2 core-shell nanostructure with a Au-Fe3O4 dumbbell nanoparticle (DB) core and SiO2/ZrO2 double shells, followed by calcination and the selective removal of the inner SiO2 shell with alkaline solution to obtain Au-Fe2O3@ZrO2 nanoreactors. The retained ZrO2 hollow (outer) shells protect the Au NPs from aggregation at temperatures up to 900 degrees C and show excellent long-term stability. Compared to Au@ZrO2 yolk-shell nanoreactors, Au-Fe2O3@ZrO2 shows improved activity in CO oxidation due to the active Au-Fe2O3 interface. This strategy can be extended to other yolk-shell nanoreactors with various nanocomposites and for different catalytic reactions
Tribological mechanism of micro-arc oxidation coatings prepared by different electrolyte systems in artificial seawater
No full textThe micro-arc oxidation (MAO) coatings were prepared in four different electrolyte systems, including mixed acid, phosphate, phosphate-aluminate and phosphate-silicate electrolytes. The friction and wear properties of MAO coatings in ambient air, seawater and four groups of saline solutions related to seawater were investigated. The results showed that the addition of silicate to phosphate could increase the density of the coating. The phosphate-aluminate ceramic layer exhibited the lowest wear rate in various environments. Additionally, the friction coefficient and wear rate of MAO coating in seawater were lower than those in ambient air, which was due to the boundary lubrication effect of seawater. Meanwhile, the presence of divalent metal salts in seawater made its lubricity better than other salt solutions
Anomalous Thermopower and High ZT in GeMnTe2 Driven by Spin's Thermodynamic Entropy
No full textNaxCoO2 was known 20 years ago as a unique example in which spin entropy dominates the thermoelectric behavior. Hitherto, however, little has been learned about how to manipulate the spin degree of freedom in thermoelectrics. Here, we report the enhanced thermoelectric performance of GeMnTe2 by controlling the spin's thermodynamic entropy. The anomalously large thermopower of GeMnTe2 is demonstrated to originate from the disordering of spin orientation under finite temperature. Based on the careful analysis of Heisenberg model, it is indicated that the spin-system entropy can be tuned by modifying the hybridization between Te-p and Mn-d orbitals. As a consequent strategy, Se doping enlarges the thermopower effectively, while neither carrier concentration nor band gap is affected. The measurement of magnetic susceptibility provides a solid evidence for the inherent relationship between the spin's thermodynamic entropy and thermopower. By further introducing Bi doing, the maximum ZT in Ge0.94Bi0.06MnTe1.94Se0.06 reaches 1.4 at 840 K, which is 45% higher than the previous report of Bi-doped GeMnTe2. This work reveals the high thermoelectric performance of GeMnTe2 and also provides an insightful understanding of the spin degree of freedom in thermoelectrics
Facile Fabrication of Flexible Pressure Sensor with Programmable Lattice Structure
No full textFlexible pressure sensors have attracted intense attention because of their widespread applications in electronic skin, human-machine interfaces, and healthcare monitoring. Conductive porous structures are always utilized as active layers to improve the sensor sensitivities. However, flexible pressure sensors derived from traditional foaming techniques have limited structure designability. Besides, random pore distribution causes difference in structure and signal repeatability between different samples even in one batch, therefore limiting the batch production capabilities. Herein, we introduce a structure designable lattice structure pressure sensor (LPS) produced by bottom-up digital light processing (DLP) 3D printing technique, which is capable of efficiently producing SS high fidelity lattice structure models in 30 min. The LPS shows high sensitivity (1.02 kPa(-1)) with superior linearity over a wide pressure range (0.7 Pa to 160 kPa). By adjusting the design parameters such as lattice type and layer thickness, the electrical sensitivities and mechanical properties of LPS can be accurately controlled. In addition, the LPS endures up to 60000 compression cycles (at 10 kPa) without any obvious electrical signal degradation. This benefits from the firm carbon nanotubes (CNTs) coating derived from high-energy ultrasonic probe and the subsequent thermal curing process of UV-heat dual-curing photocurable resin. For practical applications, the LPS is used for real time pulse monitoring, voice recognition and Morse code communication. Furthermore, the LPS is also integrated to make a flexible 4 x 4 sensor arrays for detecting spatial pressure distribution and a flexible insole for foot pressure monitoring
Copper Tannic Acid-Coordinated Metal-Organic Nanosheets for Synergistic Antimicrobial and Antifouling Coatings
No full textThe copper tannic acid (CuTA) nanosheets with an excellent antibacterial activity were successfully prepared, which showed fine antibacterial and antifouling performance after hybridization with acrylic resin. The morphology and structure characterization of CuTA nanosheets were studied by transmission electron microscopy, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, etc. The plate counting method, zone of inhibition test, and minimum inhibitory concentration (MIC) method were used to detect the antibacterial activity of the prepared samples against Gram-positive Bacillus subtilis (B. subtilis) and Gram-negative Escherichia coli (E. coli). The results showed that the killing rates of 2 and 0.5 mg/mL of CuTA powder were close to 100% after 24 h. The MIC values of E. coli and B. subtilis were 0.25 and 0.5 mg/mL, respectively. The results of morphology and element distribution of bacteria, after treating with CuTA powder, revealed that Cu2+ and TA destroyed their cell walls and inhibited the proliferation and growth of the bacteria. Furthermore, the hybrid coating of CuTA nanosheets and acrylic resin showed brilliant antimicrobial performance for E. coli and B. subtilis and antialgae properties under a lower CuTA load (<= 5%). The CuTA nanosheets with a low copper content (30.9 wt %) and low pollution have promising applications in marine antifouling coatings
Epidermis microstructure inspired mica-based coatings for smart corrosion protection
No full textTwo-dimensional (2D) graphene-like nanomaterials have gained interest in anticorrosion coatings due to their enable to act as physical barriers to aggressive species, yet 2D coatings are not always effective or sustainable. Inspired by the epidermis microstructure, herein we designed a high-performance anticorrosion coating with rapid self-healing ability via integrating the excellent adhesion property of polydopamine (PDA) and superior barrier properties of natural mica nanosheets (MNSs) for the first time. Such the coating comprises a protective hard top layer with MNSs constituents (sealing agents) and a bottom hybrid soft polymer multilayer, forming a stratified epidermis microstructure, can realize a complete restoration of coating defects under water owing to their mutual benefit. These MNSs not only can enhance the barrier performance of the coating matrix to retard the diffusion of aggressive species and hamper polymer release into water, but also induce an anisotropic diffusion to promote the self-healing of the polymer chains. The microstructures of the bioinspired coatings were systemically investigated by scanning electron microscopy (SEM) and optical microscopy (OM) measurements. Electrochemical results confirmed the anticorrosion performance of the coatings were significantly improved. This work provides a new insight for the design and fabrication of 2D nanomaterials reinforced high-performance and smart anticorrosion coatings
Oxidation behavior and electrical conductivity of MAXs phase (Ti,Nb)(3)SiC2 as a novel intermediate-temperature solid oxide fuel cell interconnect material in anode environment
No full text(Ti,Nb)(3)SiC2 possesses high oxidation resistance and electrical conductivity in cathode side, endowing it potential application as intermediate-temperature solid oxide fuel cell (IT-SOFC) interconnects. However, the performances of (Ti,Nb)(3)SiC2 in anode side must be well understood before the application comes true. In this paper, the oxidation resistance and electrical conductivity of (Ti,Nb)(3)SiC2 in simulated anode reducing atmosphere are sys-tematically investigated. The oxidation kinetics follows parabolic law with a kP value of 7.57 x 10(-14) g(2) cm(-4) s(-1). The formed single oxide layer is composed of uniformly distrib-uted Nb-doped rutile TiO2 and amorphous SiO2, without carbon deposition. High partial pressure of H-2 and CO in simulated anode reducing atmosphere inhibit the oxidation by H2O and CO2. Nb doping with strengthen the Ti-O bond can also slow down the oxidation rate. ASR of (Ti,Nb)(3)SiC2 after 605 h cyclic oxidation is 1.6 and 3.7 mc] cm(2) at 800 degrees C and 500 degrees C, respectively. The low ASR comes from the induced extra electrons by Nb doping and the dissolution of H2O and H-2 in oxide, and the integrated TiO2 conductive network in the scale. (Ti,Nb)(3)SiC2 exhibits superior performances in simulated anode reducing atmosphere, making it an promising candidate for SOFC interconnect. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved
Numerical and experimental study on the deformation of aluminum alloy ring treated by ultrasonic shot peen forming
No full textUltrasonic shot peen forming (USPF) is a promising and widely used forming technique for thin metallic parts. In this paper, detailed deformation behavior of the aluminum alloy ring caused by USPF was studied, which is of a great significance to industrial applications for roundness correction and reshaping of the ring parts, such as wheel hub, petrochemical containers, pressure vessels, and spacecraft shells. Firstly, the motion of the single pin during USPF was recorded by a high-speed camera. Then, by combining the recorded results and the stress wave theory, the firing pin motion was approximately described as an effective impact of 100 times per second and the average impact velocity of 5 m/s. By considering the firing pin movement, the 3D USPF FE model of a cell AA6061-T6 sheet was developed successfully for obtaining the accurate plastic strain field. Subsequently, a 2D USPF FE model of the ring part was developed, which is able to obtain similar residual stress profiles with the 3D cell's FE model by inputting the plastic strain profiles induced by the firing pin impact. Based on the results of experimental and numerical simulation, it was observed that the convex deformation of the ring part increases as the wall thickness decreases and the central angle of the treatment area increases. In addition, a wave contour and a local deformation with a little influence on the other area of the ring part can be achieved by three USPF treatment areas distributed in one-sided surface and two-sided surface, respectively
Ultrahigh energy storage performance of a polymer-based nanocomposite via interface engineering
No full textHigh-performance electrostatic capacitors are in urgent demand owing to the rapid development of higher power electronic applications. However, developing polymer-based composite films with both a high breakdown strength (E-b) and dielectric constant (epsilon(r)) is still a huge challenge. Here, hierarchically structured SrTiO3@SrTiO3 nanofibers (ST@ST NFs), in which crystalline SrTiO3 nanoparticles are embedded into the amorphous SrTiO3 nanofibers, are incorporated into the poly(vinylidene fluoride-co-hexafluoropropene) (P(VDF-HFP)) matrix to form a multiscale internal/external interface to break the paradox of a high epsilon(r) with decreased E-b, and that in turn gives rise to a remarkably improved energy storage capability. The percolation of the SrTiO3-SrTiO3 interfaces could promote interfacial polarization, resulting in a substantially increased epsilon(r) of the polymer nanocomposites at a rather low concentration of nanofillers. More importantly, the improved E-b of 630 MV m(-1) is also achieved through the multiscale internal/external interface. These very favorable values give rise to an ultrahigh discharged energy density (U-d) of similar to 25.26 J cm(-3), which is 283% of the value of the pure P(VDF-HFP) film. A record enhancement ratio of U-d is achieved in this work among the previously reported results to the best of our knowledge. This approach provides a new dimension of interface engineering to adjust and improve the energy storage properties of polymer nanocomposites
The DFT-ReaxFF Hybrid Reactive Dynamics Method with Application to the Reductive Decomposition Reaction of the TFSI and DOL Electrolyte at a Lithium-Metal Anode Surface
No full textThe high energy density and suitable operating voltage make rechargeable lithium ion batteries (LIBs) promising candidates to replace such conventional energy storage devices as nonrechargeable batteries. However, the large-scale commercialization of LIBs is impeded significantly by the degradation of the electrolyte, which reacts with the highly reactive lithium metal anode. Future improvement of the battery performance requires a knowledge of the reaction mechanism that is responsible for the degradation and formation of the solid-electrolyte interphase (SEI). In this work, we develop a hybrid computational scheme, Hybrid ab initio molecular dynamics combined with reactive force fields, denoted HAIR, to accelerate Quantum Mechanics-based reaction dynamics (QM-MD or AIMD, for ab initio RD) simulations. The HAIR scheme extends the time scale accessible to AIMD by a factor of 10 times through interspersing reactive force field (ReaxFF) simulations between the AIMD parts. This enables simulations of the initial chemical reactions of SEI formation, which may take 1 ns, far too long for AIMD. We apply the HAIR method to the bis(trifluoromethanesulfonyl)imide (TFSI) electrolyte in 1,3-dioxolane (DOL) solvent at the Li metal electrode, demonstrating that HAIR reproduces the initial reactions of the electrolyte (decomposition of TFSI) previously observed in AIMD simulation while also capturing solvent reactions (DOL) that initiate by ring-opening to form such stable products as CO, CH2O, and C2H4, as observed experimentally. These results demonstrate that the HAIR scheme can significantly increase the time scale for reactive MD simulations while retaining the accuracy of AIMD simulations. This enables a full atomistic description of the formation and evolution of SEI